This invention relates to a water activated adhesive composition and to an adhesive tape employing the composition.
Adhesive compositions have been employed as a coating on thin paper strips to form paper-backed adhesives employed to join the ends of paper board forms, particularly boxes. Animal glue-based adhesives have been widely used as the adhesive for such tapes.
To obtain satisfactory adhesion with water activated tapes, it is necessary that the water activated tape have the correct tack and setting characteristics. For example, it must rapidly gain tack when water activated (initial adhesion), and retain this tack for a reasonable period of time (open time) so that minor delays in applying it to a carton do not cause sealing tape failure on the resulting package. When water activated and applied to the meeting edges of folded flaps of a cardboard carton, the tape should adhere tenaciously, even prior to drying and hold the folded flaps in position against the shear forces exerted against the seal by the tendency of the folded flaps to open to their original unfolded condition (wet shear strength). After being placed in position over the flaps of a carton, and allowed to dry, the tape should form seals of high adhesive and shear strength and thus continue to effectively perform its sealing function.
In addition to the foregoing, under ordinarily encountered conditions of temperature and humidity, the gummed sealing tape should not block when shipped or stored in roll form, or as sheets stacked one on top of another, even though in such structures the water-activatable gummed layer of one sheet is in direct contact with the backing of an adjacent sheet.
Furthermore, such tapes must possess proper strength characteristics in order to be employed in present machine-automated packaging systems. In such systems, the tape is rolled from a cylindrical roll, passed over a water applicator such as a brush and then to the surface of the paper board at the desired location. If the adhesive is too tacky, it will not unroll from the paper roll at the satisfactory rate since it will stick to the adjacent paper undesirably. Furthermore, if the adhesive does not have the correct degree of tack and setting, it will become loosened within a relatively short time after application to the paper board.
Up to the present time, no synthetic-based adhesive has been found satisfactory for use as a water activated adhesive so that, up to the present time, animal glue-based adhesives have been employed uniformly. However, animal glues recently have become unsatisfactory due to a greatly increased cost. This increased cost has provided an incentive to form alternative adhesive systems.